Cryopreservation of purified bovine islets of Langerhans

In this study, bovine islets were isolated by collagenase digestion and density gradient purification, equilibrated stepwise with 3 M dimethylsulfoxide at 24 degrees C, nucleated at -150 degrees C, slow cooled at 0.25 degrees C/min down to -40 degrees C, and finally stored at -150 degrees C. After variable periods of time, the islets were quickly thawed at 37 degrees C, and dimethylsulfoxide was removed by 0.75 M sucrose. Postthawing recovery was 86 +/- 6% islet equivalents. Histology confirmed the identity and morphological integrity of the islets. Insulin release from the frozen-thawed islets was 0.13 +/- 0.03 microU/is/min at 3.3 mmol/L glucose and increased significantly (0.27 +/- 0.04 microU/is/min, P < 0.05) at 25 mmol/L glucose. Encapsulated, cryopreserved islets reversed hyperglycemia in diabetic mice after 6-8 days following implantation. Therefore, the method described in this paper permitted successful cryopreservation of bovine islets of proven in vitro and in vivo viability.